Various engine systems may use pulleys, such as the engine front end accessory drive (FEAD). In one example, the FEAD includes a serpentine belt system driving a plurality of peripheral devices, such as an alternator, power steering pump, water pump, A/C compressor, air pump, etc. Further, the belt may also be guided by an idler pulley and/or a belt tensioner (which may be spring loaded, hydraulic, or manual). In some examples, the pulley wheel is attached to an axle via spokes which are extended from the axle to the wheel, where the spokes intersect with the wheel as structural ribs traversing straight across the width of the wheel and perpendicular to the sides of the wheel.
A pulley, such as a nylon backside idler may emit a structure-borne noise corresponding the frequency and number of structural ribs when used in an automotive FEAD or other serpentine belt drive system application. The perpendicular structural ribs result in a harmonic defect on the belt running surface of the idler pulley due to material shrinkage and mold fill abnormalities. The defects on the surface of the pulley can impact the belt as it passes over the outer surface of the idler pulley, resulting in the structure-borne noise audible to the user.
In one approach, described in U.S. Pat. No. 6,648,784, an idler sprocket/pulley includes teeth, complementary to teeth of a belt in the belt drive system. The teeth of the sprocket/pulley have an arcuate pitch that substantially matches the pitch of a belt when engaged with the sprocket/pulley at the mating interface, thus accounting for the wrap angle of the belt and reducing noise generated during operation of the belt system due to reduced contact between a sprocket tooth and a belt land.
The inventors herein recognize potential issues with such an idler pulley design. As one example, in the previously described pulley, the pulley only provides noise reduction when used in combination with a specific belt. The pitch of the belt must precisely match that of the pulley in order to function in noise reduction. If a replacement belt is provided without the specific matching pitch, noise may be significantly increased.
In another example, the belt used in combination with the previously described pulley may stretch or warp as it ages. As the belt ages, the teeth of the belt may no longer precisely match the teeth of the pulley, again resulting in increased noise generation during vehicle operation.
Some of the above issues may be at least partly addressed by a belt drive system for a vehicle, comprising: a front end accessory drive including a plurality of accessory pulleys and an idler pulley rotatably coupled via a continuous belt, the idler pulley comprising, a hub which rotates around a rotational axis; a belt contacting surface on an outermost circular portion; and a plurality of angled spokes connecting the hub and the outermost circular portion.
In this example, the idler pulley may include angled ribs molded into the pulley to join the hub and an outermost circular portion. As the belt runs over the surface of the pulley, any defects on the belt running surface of the pulley due to shrinkage and fill are now angled. Angling of the defects reduces direct impact with the belt and therefore reduces the structureborne noise produced by operation of the belt and the pulley. The pulley may further include a smooth belt contacting surface, such that the pulley may be used with a belt with a variety of teeth pitches or a belt that substantially lacks teeth. Thus the pulley may provide noise reduction even as the belt ages and/or if the belt is replaced with a one of a differing tooth pitch.
In one specific example, an idler pulley includes a hub which is rotatably attached to a rotational axis of a FEAD of a vehicle. A belt contacting surface of the pulley may be smooth or include teeth, and spokes connecting the hub to the surface of the pulley may be angled relative to the sides of the pulley (non-perpendicular and non-parallel). A cross section of adjacent spokes yields a series of continuous peaks and valleys having an equal angle between each adjacent ribs and the height of the peaks and valleys is equal to the width of the belt contacting surface. As the spokes are continuous, the pulley may have greater material strength than a pulley with discontinuous spokes.
The angle between each of the adjacent spokes may range from 5° to 100°. The pulley may be used in combination with a belt with a variety of teeth pitches or a belt that substantially lacks teeth. The pulleys may also retain noise reducing capabilities even as a belt stretches or sustains defects over time and/or if the belt is replaced with one of a differing tooth pitch.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.